A wide variety of heart valve prostheses have been developed over the past several decades to serve as replacements for defective natural valves; they operate hemodynamically, as fluid check valves, in conjunction with the pumping action of the heart. These mechanical heart valves have variously had valve bodies which are designed to function together with either a valve member in the form of a single occluder or with two, three or more occluders or leaflets; in any event, the valve members generally pivot along eccentric axes (or both pivot and translate) to open and close a blood flow passageway defined by the valve body.
U.S. Pat. No. 4,689,046 (Bokros) shows a version of a bileaflet heart valve wherein each leaflet has an ear of specific shape extending from each lateral edge, which ear pivots in a recess of complementary shape. The valve is generally referred to as a side flow valve because there is a greater flow area in the regions lying between each leaflet and the surrounding valve body than in the central region between the two leaflets.
U.S. Pat. No. 4,326,304 (Klawitter) illustrates a single occluder valve wherein the occluder is made of substantially uniform thickness having a concave-convex configuration and a generally elliptical periphery to fit within a valve body having a passageway that has a generally right circular cylindrical configuration except for a pair of opposed flat sidewalls where the pivot mechanism is located. The occluder is located generally centrally of the flow passageway, and it is oriented in its open position, as shown, at an angle of about 10.degree.-15.degree. from the valve body centerline to assure prompt and reliable closing.
U.S. Pat. No. 4,425,670 (Figuera) discloses another version of a heart valve prosthesis which has a single occluder of irregular shape. The occluder is also located generally centrally within the valve passageway and is guided in its pivoting movement by pair of pegs that extend outward from the wall of the valve body and are received in cavities provided along the lateral edges of the occluder.
U.S. Pat. No. 4,775,378 (Knoch et al.) discloses a heart valve prosthesis employing a single occluder having a shape, along its centerline, generally that of an S-shaped curve. The occluder has an upstream section wherein the pivot axis is located, which section has a convex surface that faces downstream in the closed position. It is oriented at maximum opening angle of about 65.degree.-75.degree. and thus occupies a significant portion of the center of the valve passageway. U.S. Pat. No. 4,846,830 discloses a bileaflet valve having a pair of leaflets of generally similar curvature to the foregoing.
U.S. Pat. No. 4,923,465 (Knoch et al.) shows a cardiac valve prosthesis wherein a single occluder is journaled by a pair of laterally extending pins that are received in holes that extend completely through the wall of the valve body. The occluder itself has a composite S-shaped curvature. As shown in FIGS. 2 and 3, the occluder obscures a large portion of the central region of the valve passageway in the open position, likely creating a region of dead flow downstream therefrom.
U.S. Pat. No. 5,108,425 to Hwang discloses a bileaflet valve employing a pair of leaflets having generally flat upstream sections and complex curvature in their downstream sections to promote aerodynamic performance. U.S. Pat. No. 4,872,875 shows an earlier version of such a bileaflet valve.
U.S. Pat. No. 4,423,525 (Vallana et al.) shows a single occluder valve where the occluder is free to rotate about its central axis and is guided in its pivoting action by protrusions that extend from the annular valve body. If the occluder were to be oriented parallel to the central axis, as illustrated in FIG. 2, it would not be assured to close promptly and reliably.
U.S. Pat. No. 5,314,467 shows a bileaflet valve having leaflets of a composite curvature which both pivot and translate in moving between their open and closed positions, guided by recesses in the sidewall of the valve body that receive ears extending from the lateral edges of the leaflets. The guiding recesses are described as each having one epicycloid-serpentine shaped sidewall and one concave sidewall.
U.S. Pat. No. 4,820,299 discloses a tri-leaflet cardiac valve having three "flaps" that are essentially 120.degree. segments of relatively smooth curvature. Pivoting motion is controlled by spurs 17, 18 and 19, the central one of which interengages with a stirrup 16 and magnetic masses at the corners of the flaps can be used to assist movement.
U.S. Pat. No. 5,207,707 discloses a tri-leaflet valve wherein the leaflets have an essentially flat main body which meet at a central point in the closed position. The pivot recesses are located in three interior protrusions and constitute curved grooves that accommodate ears 74 that are fashioned from the canted edge sections of each leaflet. The valve presents a generally triangular shaped special opening in its open position; however, there is no guarantee that the leaflets will promptly close or will simultaneously close.
Commercially developed heart valves have employed several designs similar to those set forth in various of the aforementioned U.S. patents; however, all such commercially feasible designs are felt by those working in this field to have various shortcomings compared to the fluid dynamic performance of the natural heart valves for which they are substituting. Further improvements are felt necessary particularly with respect to fluid flow rate and pressure drop through the valve body, to reducing the volume of blood which regurgitates upon reversal of flow, e.g., at the end of a pumping stroke, to the ability of the valve to operate in a thrombus-free fashion for the life of the patient, and to the ability to avoid regions of turbulence and potential blood damage. As a result, improvements in valve construction have continued to be sought with the objective of creating mechanical valves with flow characteristics such that there is minimum resistance to blood flow and/or damage to blood itself, which valves close promptly upon the termination of the pumping stroke with only low regurgitation.